Nolinear Output Characteristics Research Of Superheterodyne Receiver System

The Mathematical model can describe the output characteristics and reflect the working state under interference conditions of the superheterodyne receiver system.It provides the theoretical basis for improving the performance and anti-interference ability of the receiver system.Taking the S-mode signal receiver in multipoint positioning system as the research object,the simplified frequency-domain Volterra series is used to analyze the nonlinear characteristics of S-mode signal receiver.The results show that when analyzing the output characteristics of nonlinear systems such as S-mode signal receiver,the simplified frequency-domain Volterra series has high accuracy and low amount of calculation.First,the polynomial model is obtained by simplifying the time-domain Volterra series.The mixer system and power amplifier system are selected as the research objects respectively,and the circuits are simulated.The polynomial model is used to analyze their output characteristics.Then,the simplified frequency-domain Volterra series is theoretically deduced and complemented,and the calculation formula and limiting conditions are determined when the band-limited signal is input;The error rates of mixer system model and power amplifier system model based on simplified frequency-domain Volterra series are analyzed respectively;The circuit system with iron core inductance is simulated,the model error rates of iron core inductance system based on different orders of simplified frequency-domain Volterra series are analyzed,and the factors affecting the model error rates are summarized.The results show that the minimum error rate of the core inductance system model based on the simplified frequency-domain Volterra series is 0.2%.The calculation amount of the tenth order simplified frequency-domain Volterra series is only 410 times,which is far lower than that of the complete form Volterra series.Finally,the output characteristics of superheterodyne receiver system are analyzed by using simplified frequency-domain Volterra series.By inputing different S-mode signals,the model error rates of S-mode signal receiver system based on simplified frequency-domain Volterra series are analyzed.When the S-mode signal without noise is input,the error rate of the simplified model is less than 3%;With the S-mode signal with 15 d B noise input,the minimum error rate of the simplified model is less than 18.23%;When the S-mode signal with 10 d B noise is input,the error rate of the simplified model is high.The S-mode signal with 10 d B noise is predistorted,and the error rate of the simplified model is reduced from100% to 18.05%;When the measured S-mode signal with signal-to-noise ratio of 16.25 d B is input,the error rate of the simplified model is about 12%.It shows that the S-mode signal receiver system based on simplified frequency-domain Volterra series can accurately describe the output characteristics of superheterodyne receiver system,and the error rate of the simplified model can be significantly reduced after preprocessing the S-mode signal with high-power noise.